When migrating mailboxes from Exchange Hybrid to Exchange Online (O365), you may receive the below error when attempting to migrate a new batch
The maximum number of migration batches is already running. Please remove a batch before you add another one.
The limit of the number of migration batches you can create is 100. The main purpose of why Microsoft set this limit is for performance reasons. Having more than 100 batches causes performance problems and could cause outages for other customers in the multi tenant system. You can check the limit by typing the below command within Exchange Online Powershell
Get-MigrationConfig |FL *max*
This error is common when migrating mailboxes from Exchange to O365 (Exchange Online) and users find that when they receive this error there are no other migration batches in progress.
This 100 batch number limit also includes batches which have already been completed. To get around this, remove a completed batch and start your new batch migration again. You’ll find that it works.
Please do comment below to let us know how you get on